In a range of different scenarios involving someone who has done wrong – a negligent friend; a criminal offender; and a troubled personal relationship – Dr Strelan and colleagues found that people were more willing to forgive if those who had offended against them had been punished in some way.

"Justice and forgiveness are often considered to be opposites, but we've found that victims who punish their offender are more able to forgive and move on," Dr Strelan says.

"Punishment could take many different forms. It could be giving someone the 'silent treatment', which in itself is a very powerful psychological punishment. Or in the case of a criminal offender, knowing that a court of law has imposed a reasonable sentence and that justice is being done – that may be enough for some people to forgive.

"That sense of justice, or getting 'just deserts', is important. However, in interpersonal relationships punishment should not be extreme or vengeful – if it were, this would not help to repair the damage in the relationship and is likely to make things worse.

"For forgiveness to really work, there must be a sense that negative responses towards a transgressor are being replaced with positive ones. It's not about retaliation, it's about responding constructively and doing something about people's poor behavior toward you, in a way that works for both parties involved in the conflict," he says.

Dr Strelan says many people have a difficult time forgiving those who have done them wrong.

"When you get hurt by someone you naturally feel vulnerable, and the very idea of forgiving someone also makes a victim feel vulnerable. When some form of punishment is involved, the victim feels more empowered by that and is more able to forgive," he says.

As well as providing a better understanding of human behavior and emotions, Dr Strelan's research could help to inform clinical psychologists and relationship counselors.